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</pre><pre class="rust ">
<span class="doccomment">//! A macro for defining #[cfg] if-else statements.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! The macro provided by this crate, `cfg_if`, is similar to the `if/elif` C</span>
<span class="doccomment">//! preprocessor macro by allowing definition of a cascade of `#[cfg]` cases,</span>
<span class="doccomment">//! emitting the implementation which matches first.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! This allows you to conveniently provide a long list #[cfg]&#39;d blocks of code</span>
<span class="doccomment">//! without having to rewrite each clause multiple times.</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # Example</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! ```</span>
<span class="doccomment">//! #[macro_use]</span>
<span class="doccomment">//! extern crate cfg_if;</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! cfg_if! {</span>
<span class="doccomment">//!     if #[cfg(unix)] {</span>
<span class="doccomment">//!         fn foo() { /* unix specific functionality */ }</span>
<span class="doccomment">//!     } else if #[cfg(target_pointer_width = &quot;32&quot;)] {</span>
<span class="doccomment">//!         fn foo() { /* non-unix, 32-bit functionality */ }</span>
<span class="doccomment">//!     } else {</span>
<span class="doccomment">//!         fn foo() { /* fallback implementation */ }</span>
<span class="doccomment">//!     }</span>
<span class="doccomment">//! }</span>
<span class="doccomment">//!</span>
<span class="doccomment">//! # fn main() {}</span>
<span class="doccomment">//! ```</span>

<span class="attribute">#<span class="op">!</span>[<span class="ident">no_std</span>]</span>

<span class="attribute">#<span class="op">!</span>[<span class="ident">doc</span>(<span class="ident">html_root_url</span> <span class="op">=</span> <span class="string">&quot;http://alexcrichton.com/cfg-if&quot;</span>)]</span>
<span class="attribute">#<span class="op">!</span>[<span class="ident">deny</span>(<span class="ident">missing_docs</span>)]</span>
<span class="attribute">#<span class="op">!</span>[<span class="ident">cfg_attr</span>(<span class="ident">test</span>, <span class="ident">deny</span>(<span class="ident">warnings</span>))]</span>

<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">cfg_if</span> {
    ($(
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">meta</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="op">*</span> }
    ) <span class="kw">else</span> <span class="op">*</span> <span class="kw">else</span> {
        $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it2</span>:<span class="ident">item</span>)<span class="op">*</span>
    }) <span class="op">=&gt;</span> {
        <span class="macro">__cfg_if_items</span><span class="macro">!</span> {
            () ;
            $( ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">meta</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="kw-2">*</span>) ), )<span class="op">*</span>
            ( () ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it2</span>)<span class="kw-2">*</span>) ),
        }
    };
    (
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_met</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_it</span>:<span class="ident">item</span>)<span class="op">*</span> }
        $(
            <span class="kw">else</span> <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_met</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>)]</span> { $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_it</span>:<span class="ident">item</span>)<span class="op">*</span> }
        )<span class="op">*</span>
    ) <span class="op">=&gt;</span> {
        <span class="macro">__cfg_if_items</span><span class="macro">!</span> {
            () ;
            ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_met</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">i_it</span>)<span class="kw-2">*</span>) ),
            $( ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_met</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e_it</span>)<span class="kw-2">*</span>) ), )<span class="op">*</span>
            ( () () ),
        }
    }
}

<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">__cfg_if_items</span> {
    (($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>:<span class="ident">meta</span>,)<span class="kw-2">*</span>) ; ) <span class="op">=&gt;</span> {};
    (($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>:<span class="ident">meta</span>,)<span class="kw-2">*</span>) ; ( ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">meta</span>),<span class="kw-2">*</span>) ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) ), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=&gt;</span> {
        <span class="macro">__cfg_if_apply</span><span class="macro">!</span> { <span class="ident">cfg</span>(<span class="ident">all</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>,)<span class="op">*</span> <span class="ident">not</span>(<span class="ident">any</span>($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>),<span class="kw-2">*</span>)))), $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="op">*</span> }
        <span class="macro">__cfg_if_items</span><span class="macro">!</span> { ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">not</span>,)<span class="op">*</span> $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>,)<span class="kw-2">*</span>) ; $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">rest</span>)<span class="op">*</span> }
    }
}

<span class="attribute">#[<span class="ident">macro_export</span>]</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">__cfg_if_apply</span> {
    (<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>:<span class="ident">meta</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>:<span class="ident">item</span>)<span class="kw-2">*</span>) <span class="op">=&gt;</span> {
        $(<span class="attribute">#[<span class="macro-nonterminal">$</span><span class="macro-nonterminal">m</span>]</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">it</span>)<span class="op">*</span>
    }
}

<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
    <span class="macro">cfg_if</span><span class="macro">!</span> {
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> {
            <span class="kw">use</span> <span class="ident">core</span>::<span class="ident">option</span>::<span class="prelude-ty">Option</span> <span class="kw">as</span> <span class="ident">Option2</span>;
            <span class="kw">fn</span> <span class="ident">works1</span>() <span class="op">-&gt;</span> <span class="ident">Option2</span><span class="op">&lt;</span><span class="ident">u32</span><span class="op">&gt;</span> { <span class="prelude-val">Some</span>(<span class="number">1</span>) }
        } <span class="kw">else</span> {
            <span class="kw">fn</span> <span class="ident">works1</span>() <span class="op">-&gt;</span> <span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="ident">u32</span><span class="op">&gt;</span> { <span class="prelude-val">None</span> }
        }
    }

    <span class="macro">cfg_if</span><span class="macro">!</span> {
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">foo</span>)]</span> {
            <span class="kw">fn</span> <span class="ident">works2</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">false</span> }
        } <span class="kw">else</span> <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> {
            <span class="kw">fn</span> <span class="ident">works2</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">true</span> }
        } <span class="kw">else</span> {
            <span class="kw">fn</span> <span class="ident">works2</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">false</span> }
        }
    }

    <span class="macro">cfg_if</span><span class="macro">!</span> {
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">foo</span>)]</span> {
            <span class="kw">fn</span> <span class="ident">works3</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">false</span> }
        } <span class="kw">else</span> {
            <span class="kw">fn</span> <span class="ident">works3</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">true</span> }
        }
    }

    <span class="macro">cfg_if</span><span class="macro">!</span> {
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> {
            <span class="kw">use</span> <span class="ident">core</span>::<span class="ident">option</span>::<span class="prelude-ty">Option</span> <span class="kw">as</span> <span class="ident">Option3</span>;
            <span class="kw">fn</span> <span class="ident">works4</span>() <span class="op">-&gt;</span> <span class="ident">Option3</span><span class="op">&lt;</span><span class="ident">u32</span><span class="op">&gt;</span> { <span class="prelude-val">Some</span>(<span class="number">1</span>) }
        }
    }

    <span class="macro">cfg_if</span><span class="macro">!</span> {
        <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">foo</span>)]</span> {
            <span class="kw">fn</span> <span class="ident">works5</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">false</span> }
        } <span class="kw">else</span> <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> {
            <span class="kw">fn</span> <span class="ident">works5</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> { <span class="bool-val">true</span> }
        }
    }

    <span class="attribute">#[<span class="ident">test</span>]</span>
    <span class="kw">fn</span> <span class="ident">it_works</span>() {
        <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">works1</span>().<span class="ident">is_some</span>());
        <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">works2</span>());
        <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">works3</span>());
        <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">works4</span>().<span class="ident">is_some</span>());
        <span class="macro">assert</span><span class="macro">!</span>(<span class="ident">works5</span>());
    }
}
</pre>
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